Acoustic resistor



Jan. 22, 1957 SCHENKEL ET AL 2,778,440

ACOUSTIC RESISTOR Filed March 13, 1953 INVENTORS GERRIT SQHENKEL JACOB ISAAK DE HAAN AGENT United States Patent "ice ACOUSTIC RESISTOR Gerrit Schenlrel and Jacob Izaak de Haan, Eindhoven, Netherlands, assignors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application March 13, 1953, Serial No. 342,144

Claims priority, application Netherlands April 3, 1952 3 Claims. (Cl. 18132) The invention relates to acoustic resistors made of wound tape or web-like material, the flow resistance to the vibrating air being formed by narrow ducts between the separate layers of the tape or web-like material. The manufacture of such an acoustic resistor constitutes a comparatively difiicult problem in view of the mutually equidistant arrangement of the said layers.

The object of the invention is to provide a simple solution of this problem.

The acoustic resistor according to the invention is characterized in that each layer is constituted by at least one strip of material which has a flat wire or a tape wound on it with intermediate spacing. This Wire or tape is the means by which the layers are kept spaced apart, the simplicity of this means lying in the continuity of the means interposed between adjacent layers. In one embodiment each layer is constituted by two strips, only one of which has a Wire or tape wound on it, the windings on the two strips being arranged either on edge or flat. In addition, the invention relates to an acoustic device, for example a microphone, comprising an acoustic resistor, more particularly an electro-dynamic microphone comprising a dome-shaped diaphragm and an acoustic network on the the rear of the diaphragm. According to the invention a resistor element of this network is constituted by the acoustic resistor described hereinbefore, the strips of which engage each other at their broad sides so as to form a spiral and which is caused to become arcuate in a manner such that the diaphragm and the resistor are spaced by a constant distance.

The invention will now be described with reference to the accompanying diagrammatic drawing, in which three embodiments thereof are shown by way of example, and in which:

Fig. 1 is a plan view of an embodiment of an acoustic resistor according to the invention;

Fig. 2 shows for the sake of clarity an elevation of the two layers from which the resistor is built up.

Fig. 3 shows part of an electrodynamic microphone Patented Jan. 22, 1957 comprising an accoustic resistor according to the invention.

Referring now to Fig. 1, a core 1 has two strips 2 and 3 wound flat on it so as to form a spiral. The strip 3 has a flat wire or tape 4 wound on it with an intermediate spacing 5. (See also Fig. 2.)

When the strips are wound a circular body is obtained, which is characterized by the provision of narrow ducts parallel to the axis of winding, the diameter of said ducts being determined by the thickness of the said flat wire or tape 4.

Fig. 3 shows part of an electrodynamic microphone comprising a dome-shaped diaphragm 6 having secured to it a voice coil 7 arranged in the air-gap between two concentric pole pieces 8 and 9 of a magnet system, the remaining part of which is not shown. The pole piece 9 supports an acoustic resistor 10 according to the invention. This resistor is also dome-shaped and the spacing 11 between the diaphragm and the resistor is constant.

What we claim is:

1. An acoustic resistor comprising a body constituted of a plurality of layers of strip-like material wound in a spiral shape, at least one of said layers having a strip and an elongated member wound at spaced intervals about said strip, the spacings of said elongated member being narrow air passages in said body extending parallel to the central axis of said body.

2. An acoustic resistor comprising a substantially flat body constituted of two spirally-wound strip-like members and an elongated member wound at spaced intervals about only one of said strip-like members and abutting the other strip-like member, said strip-like members and elongated member defining narrow air passages in the body extending parallel to the central axis thereof.

3. In an electrodynamic microphone, a dome-shaped diaphragm and an acoustic resistor mounted behind said diaphragm, said resistor comprising a dome-shaped body constituted of two spirally-wound strips and a third strip wound at spaced intervals about only one of said two strips and abutting the other strip, said strips dcfining narrow air passages spaced along its length and extending at right angles to the surface of said diaphragm, said diaphragm and resistor being spaced apart by the same distance along all of their confronting surfaces.

References Cited in the file of this patent UNITED STATES PATENTS 1,488,565 Stewart et a1. Apr. 1, 1924 1,954,966 Thuras Apr. 17, 1934 1,975,637 Finley Oct. 2, 1934 2,065,751 Scheldorf Dec. 29, 1936 2,126,254 Garwell Aug. 9, 1938 2,656,585 Jackson Oct. 27, 1951 

